Electronic packaging utilizes stamped and formed terminals such as posts, pins, sockets, and the like fitted into the holes of printed circuit boards and soldered thereto as a principal means of interconnection. It is common practice to provide solder on such terminals by means of electrodeposition or a coating of molten solder, which is then reflowed by the application of heat to the terminals after they have been mounted to the board. The resulting reflowed solder electrically and mechanically fixes the terminals to the board, the solder flowing into engagement with circuit traces in or on the board. With respect to many designs, there is a need for substantial quantity of solder and, therefore, for a substantial thickness of solder placed on the terminal. With respect to many applications, the purer the solder alloy in terms of the presence of organic compounds therein, the better the solder with respect to long-term reliability.
Methods and apparatus for applying solder coating to conductive surfaces are well-known. U.S. Pat. No. 3,006,318 granted Oct. 31, 1961 to an apparatus for applying solder coating to surfaces teaches the use of a pair of rollers which are immersed in solder baths and spaced apart to receive a printed circuit board passed therebetween with the rollers transferring molten solder from the bath to coat the printed circuit board. Differentiation for selectivity of solder application is provided by virtue of the conductive printed circuits which are etched out on a non-conductive board material. Fluxing is provided by brushes positioned above the rollers to engage the printed circuit board in its downward travel through the rollers.
U.S. Pat. No. 4,836,131 granted Jun. 6, 1989 for a solder coating apparatus teaches the use of rollers for applying liquid solder to opposite sides of the leads of a lead frame having integrated circuit devices thereon. The solder bath is disposed below the roller assembly with the lead frames passed upwardly through the nip of the rollers. This patent teaches the use of rollers that squeeze the lead section between the rollers and apply a uniform coating of solder to opposite sides of the lead frame without causing a bridging of solder between the leads. With respect to Patent 4,836,131, the lead frames are run through the soldering apparatus twice to coat the leads on the four sides of the integrated circuit package.
It is an object of the present invention to provide an improvement through method and apparatus for solder coating electrical terminals with respect to speed of application, evenness of application, and control of thickness.
It is a further object of the invention to provide an improved method and apparatus for solder coating of electrical terminals in continuous strip form and on both sides of the terminal strip simultaneously.
It is yet a further object to provide a novel method of solder coating and an apparatus therefor that is simple, reliable, and suitable for high-volume production.